Recently, the aspect ratio of heavy-duty tires used for trucks and buses is now being reduced. Particularly, in many cases of tires with an aspect ratio of 60% or less, a circumferential-direction reinforcing belt layer having a cord angle of substantially 0° to a tire circumferential direction is disposed between crossed belt layers (see, for example, Patent Document 1). In such a belt structure, the cord tension at an edge portion of the circumferential-direction reinforcing belt layer is high. Accordingly, the cords at the edge portion of the circumferential-direction reinforcing belt layer are susceptible to a fatigue rupture. In order to avoid this problem, the widths of the crossed belt layers are made greater than the width of the circumferential-direction reinforcing belt layer, and these crossed belt layers are stacked so as to directly come into contact with each other at the outer sides, in a width direction, of the circumferential-direction reinforcing belt layer. Furthermore, an edge-portion buffering layer, so called belt edge cushion, is interposed between edge portions of the crossed belt layers. In this case, the crossed belt layers function on the outer sides, in the width directions, of the circumferential-direction reinforcing belt layer, thus reducing the cord tension in the edge portion of the circumferential-direction reinforcing belt layer. As a consequence, the fatigue rupture can be inhibited.
However, to prevent the growth of the outer-diameter of a shoulder portion of a pneumatic tire, a circumferential-direction reinforcing belt layer needs to be extended to the vicinity of the shoulder portion. Furthermore, in order to obtain the effect of inhibiting a fatigue rupture at an edge portion of a circumferential-direction reinforcing belt layer as described above, crossed belt layers need to be extended to the vicinity of a buttress portion. When the crossed belt layers are extended to the vicinity of the buttress portion, shear strain that acts on the crossed belt layers becomes large, and a separation between a cord and rubber is likely to occur at the edge portions of the crossed belt layers. Patent Document 1: Japanese patent application Tokuhyo No.